Earthbags are so much easier than adobe blocks.
In Indiana, I built something like this:
http://www.greenhomebuilding.com/riceland.htm
I used burlap bags, and added cement to my sandy loam soil; even after the burlap rotted, the "bricks" still looked good.
However, I added a real roof to it (similar to the way you would roof a hexagonal gazebo), with a two foot overhang. There was good drainage all the way around and keeping the sides from getting wet seemed to protect it very well. Based on what it looks like after 5 years, I wouldn't be surprised if it's still there in 50 years, or as long as the roof holds up.
In summer, I put a fan in one window, pointing to the outside, and drew in colder air at night, which dramatically cooled the structure on all but a few days a year. The structure would stay cool almost all day.
The drawback was that I didn't plan for solar heating; I should have had a big window on the south side. It was pretty cold all winter.
The good news was that it cost less than $200 to build, and I think it will last 20 years.
My photos were taken on film and are packed away somewhere; if I find them this weekend, I'll scan them and post.
It is a WAY fun project, I will admit.
And, viewing those photos makes me feel so blessed, even in the circumstances I find myself, post-divorce.
Thanks for the reminder of just how lucky we are.